Carrier telegraph system



June G, 1931.

Rec. Zoop Current Detector Plate Current (Mis) ATTORNEY v Patented June 16, 1.931

UNITI-:D STATES PATENT. oFFlcE VAUGEN P. THORP, OF .RIVER EDGE, NEW JERSEY, ASSIGNOR TO AMERICAN TELE- PHONE TELEGBAPH COMPANY, A CORPORATION OF NEW YORK CARRIER. TELEGRAPH SYSTEM Application led August 5, 1929. Serial No. 883,557.

This invention relates to carrier telegraph' utilize sensitive receiving relays, which are' biased to spacing by a current which has a magnetic edect on the armature of the relay of about one half that of the marking or received rectified current. This biasing'current is approximately constant and is independent ofthe line characteristics since it is supplied from a local battery. It is evident; therefore, that any change in the received current from the distant end will cause bias or distortion in the telegraph signals in the receiving loop circuit. In certain types of service, such as high speed printing telegraph service, this may be suiiiciently large to cause trouble. Accordingly it is one of the primary objects of the invention to provide arrangements whereby variations in the rea ceived currents due to changes in line attenuation or to other causes will not cause bias or distortionin the signals in the receiving loop circuit.

The arrangements of the invention utilize ra separate carrier frequency which is sent over the same line with the carrier frequencies used for signaling purposes. This separate carrier is amplified and rectified at the distant end of the line. The rectified current thus obtained is passed through a resistance and the voltage drop across this resistance, after being properlyfiltered, is used to furnish thenegative potential for the detector tubes in the telegraph channel terminals.

By this means the operation of the detector tubes may be controlled in accordance with anyl changes in the received current andthe output of the detector tubes may be substantially constant. Further objects and features of the invention will appear more fully from the detailed description thereof hereinafter given.

The invention ma be more fully understood from the fol owing description together with the accompanying drawings in the Figs. 1, 2 and 3 of which the invention is illust-rated. Fig. 1 is a circuit diagramv illustrating a preferred embodiment of the invention. Figs. 2 and 3 illustrate graphically certain characteristics of the 'received telegraph signals under various vline conditions. v

In Fi .'1 is shown a transmission line 1, at

each en of which would be provided terminal apparatus similar to that shown at only one end thereof in the'drawing. The line 1 would be connected through a transformer 2 to a common sending circuit 3 to which might be connected a plurality of lines such as 5 and 6 whereby different carrier frequency channels might be transmit-ted over lme 1. rlhere would also be provided a circuit 7 connected to a source such as 8, whereby a' separate carrier .frequency might be continuously applied to the line and transmitted thereover with the carrier frequencies used for signaling purposes. The line 1 would also be connected to a common receiving circuit 4 to which there would be connected individual receiving circuits such as 9 and 14. Circuit 9 would include a filter 10, an amplifier 11, which would be connected to the input of a detector 12. The output of this detector would be connected to a receiving relay. Circuit 14 would be of a similar nature and only the filter 15 thereof is shown.

An additional receiving circuit such as 16 would bey provided and would be connected to circuit 4. This receiving circuit will be rendered selective by thev filter .17 for` the separate carrier frequency transmitted over line 1 from the distant station from the gendevice 21 and then utilized to furnish the negative potential for the detector tube 12. By means of other connections, such as 22, this voltage drop may be used to furnish the negative potential for the detector tubes in other of the receiving circuits.

When the system is properly lined up, the

y negative grid potential for the detectors in the various telegraph channel terminals will be adjusted to a certain predetermined value. If the line attenuation subsequently increases, the received carrier current input to each telegraph channel terminal will be reduced. With a constant negative grid potential supplied to the detector tubes, as in former types of systems, the detector plate current will change its rate of build-up from that shown on curve a to that indicated on curve b of Fig. 2. The receiving relay would then operate at points m and n instead of at points p and g which, as shown in Fig. 3, would cause distortion in the form of spacing bias. Ifthe line attenuation decreases the received current would build up along curve c instead of a which would cause the relay to operate at points 1' and s, thus causing distortion in the orm of marking bias.

If, instead of maintaining a constant negative grid potential for, the channel terminal detector tubes, the arrangements of the invention as shown in Fig. 1 are used, then the detector grid potentials will also be affected by changes in line attenuation in such a way as to tend to shift curves b and c to the position occupied by a which is the `one necessary for unbiased signals. rihe circuits may be so adjusted that over a fairly wide variation of line attenuation, the detector plate current which operates the receiving relay will not only have a constant maximum value but will also build up at the same rate as before the attenuation change took place. It is pointed out that the steady carrier used for the grid potential supply need occupy only a small portion of the frequency range available for telegraph purposes since no appreciable band width is necessary. It would be desirable probably to locate this carrier frequency midway in the frequency range used for the telegraph receiving circuits tominimize the effect of difference in attenuation changes with frequency.

In addition to compensatingv for line at tenuation changes, the circuit arrangements of this invention takes care to some extent of the change in battery voltages at the terminal stations. At the sending station, forexample, the oscillator and sending amplifier supplyingthe steady carrier current will vary in output with changes in battery potentials and at the receiving station the gain -of the receiving vamplifier will likewise vary' with battery potential chan In each 'case the grid potential on the etector tubes will be shifted in the proper direction to correct to selectin some degree for these local variations in batl plurality of Idi'erent carrier frequency cur-I rents over the system, separately detecting said received carrier currents, simultaneously transmitting over the same system a separate carrier frequency current, and utilizing said separate carrier frequency current to control said detection. I

2. In a carrier telegraph system the method of signaling which comprises transmitting a plurality of different carrier frequency currents over the system, separately detecting said received carrier currents, simultaneously transmitting over the same` system a'separate carrier frequency current, and utilizing said separate carrier frequency current to control the negative grid potential Yof the tubes utilized for said detection.

3. A carrier telegraph system comprising a line interconnectin two stations, means at one of said stations or applying to saidv line a plurality of carrier frequency currents for signaling purposes, means at said station for applying a separate carrier frequency current to said line, means at the other of said stations for selecting and separately detecting said plurality of carrier frequency signaling currents, means at said last station for selecting said separatecarrier frequency current and for utilizing said current to control the output' of said detections.

a plurality of carrier frequency currents for signaling purposes, means at said station for applying a vseparate carrier frequency current to said line, a receiving circuit at the other of said stations comprising means for selecting said first named carrier frequency currents and aseparate detector for each carrier frequency, a receiving circuit at said last mentioned station comprising means for said separate carrier frequency means in said circuit for rectifying said separate carrier frequency and means for controllin the output of said detectors by said recti ed current.

5.v A carrier telegraph system comprising a line interconnecting two stations, means at one of said stations for applying to said line a plurality of 4diierentcarrier frequency currents for signaling purposes,means at said station for applying a separate carrier freiis quency current to said line, a plurality of receiving circuits at the other of said stations each comprising means for selecting different ones of said plurality of carrier currents and cach of said receiving circuits including vacuum tube detectors, a receiving circuit at said last mentioned station comprising means selective for said separate carrier frequency, a rectifier in said last mentioned receiving circuit, a resistance bridged across said rectiier output, and means'for utilizing the voltage drop across said resistance to control the negative grid potential of all of said detectors.

6. A. carrier telegraph system comprising a line interconnecting two stations, means at one of said stations-for applying to said line a plurality of carrier frequency currents Jfor signaling purposes and a pilot carrier .frequency, a. separate receiving circuit at the other station for each signaling channel and each comprising a detector, a rectifier for the pilot carrier, a resistance in the output thereof, and a condenser shunted around said resistance, the drop in E. M. F.- across the resistance constituting a portion of the grid bias of each detector.

7. A carrier telegraph system comprising a line interconnecting two stations, means at one of the said stationsy for applying to said line a plurality of carrier frequency currents for signaling purposes, means at said station for applying a pilot carrier current to said line, a separate receiving circuit at the other station in each signaling channel each comprising a-detector, a rectifier for the pilot carrier and afresistance in the output thereof, the inputijcircuitJ-of each detector comprising an individual transformer Winding and the reetifierresis'tance being in series therewith andlcommon to all the detectors.

ln testimonywhereof, I have signed my name to this specification this 30th day of July, 1929.

VAUGHN THORP. 

